Add blob sidecar index field

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 2.95%. Comparing base (b94d32c) to head (4ddf258). Report is 102 commits behind head on main.

Files	Patch %	Lines
eth/pubsub.go	0.00%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #29 +/- ## ======================================== - Coverage 7.75% 2.95% -4.80% ======================================== Files 7 26 +19 Lines 400 3755 +3355 ======================================== + Hits 31 111 +80 - Misses 361 3633 +3272 - Partials 8 11 +3 ```

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